One way is to absorb all the light that hits you! Then none will get back to the eyes of the person looking at you.
Problem
They wouldn’t see you, but there would be a black, you-shaped hole where you were, like a shadow. That is what blackness is – no light coming from that place!
It works for Submarines!
A very similar idea has been used for years to make submarines invisible to sonar. Light doesn’t travel well through water but sound does, so we use sound to see underwater: Sonar.
Sonar involves ships sending out pings of sound, then listening for the sound that bounces back to show what is there (just like bats).
To make themselves invisible to sonar, submarines can be covered in a surface that absorbs the sound instead of bouncing it back. This works if they are in deep sea as there is nothing behind them to bounce pings back: the sound equivalent to blackness behind.
Stealth planes use the same idea to make themselves invisible to RADAR!
A bit of cs4fn 